This research is directed toward developing predictive mathematical models on aerosol deposition in the human respiratory system for occupational application. The main emphasis will be placed upon intersubject variability due to variations in lung geometry, breathing pattern and physiological conditions. Deposition and this frequency distribution in different regions of the respiratory system will be obtained when breathing under various work-load conditions and for a wide range of particle sizes. Information on polydisperse aerosols will also be provided.